Nb-doped Sr₂Fe_1.5Mo_0.5O_6-δ electrode with enhanced stability and electrochemical performance for symmetrical solid oxide fuel cells

In this study, Nb doped double perovskite oxide (Sr₂Fe_1.4Nb_0.1Mo_0.5O_6-δ)is prepared and tested as symmetrical electrodes for intermediate temperature solid oxide fuel cells. X-ray diffraction demonstrates that Sr₂Fe_1.4Nb_0.1Mo_0.5O_6-δ maintains more stable cubic perovskite phase structure than its raw material (Sr₂Fe_1.5Mo_0.5O_6-δ)under reducing atmosphere. X-ray photoelectron spectrometry shows that Nb doping significantly enhances bond strength of Fe[sbnd]O[sbnd]Fe(Nb)so that Fe ion maintains more stable oxidation states after reducing. At 600 °C, Nb doping also increases the conductivity from 17.62 to 27.61 cm⁻¹ in air and from 11.11 S cm⁻¹ to 15.86 S cm⁻¹ in wet hydrogen (∼3% H₂O). Furthermore, Sr₂Fe_1.4Nb_0.1Mo_0.5O_6-δ exhibits enhanced electrochemical performances in terms of lower polarization resistance under both oxidizing and reducing atmospheres. Peak power densities of 364.93 and 531.49 mW cm⁻² at 750 and 800 °C are obtained based on a single symmetrical cell with Sr₂Fe_1.4Nb_0.1Mo_0.5O_6-δ electrode, which also shows excellent redox stabilities. All of these results confirm that Sr₂Fe_1.4Nb_0.1Mo_0.5O_6-δ electrode has promising prospects for the symmetrical intermediate temperature solid oxide fuel cells.